You’ve heard them all before – cut out the carbs, sit down while you eat, sugar is the enemy – but are they true. Dr Wynnie Chan explains why these well-known fallacies are far from fact

Myth 1: You can’t have sugar, fat or alcohol if you’re on a diet
The main goal of a diet is to eat fewer calories than you need to maintain your current body weight. For most of us who want to lose weight permanently, we should follow a diet or eating plan that is nutritionally sound, tasty and not based on a single or limited range of foods.

A realistic diet will not restrict certain foods or ingredients (especially our favourite ones) like sugar, fat and alcohol across the board, as this will only make you feel deprived. For many people, an eating plan that doesn’t allow the occasional treat is a short-lived one. Additionally, if you severely restrict your calories while dieting, then once you stop the diet and begin to eat these foods again (which is inevitable), you will likely gain the weight back. This is because your metabolism slowed during the diet and you won’t be able to efficiently burn the amount of calories you’re now consuming.

Because many people find they can stick to a long-term diet if they’re allowed the odd sugary ‘treats’, many successful weight loss programmes, such as Weight Watchers, allow sweets. If you have a sweet tooth or drink alcohol regularly, the most effective way to reduce your intake is to phase out these items gradually. This might mean cutting down on ‘visible sugar,’ such as the pure kind you put in tea or coffee. For alcohol, it might mean alternating alcoholic drinks with non-alcoholic ones.

Myth 2: Meal replacements are the best way to lose weight because they help shrink your stomach.
Meal replacements, like Slimfast or other similar very low calorie diets (VLCD), usually come in the form of a high-protein, low-fat drink. Meal replacement plans are designed to be followed for a short period of time – weeks or sometimes even days – and they encourage rapid weight loss. These plans, which usually provide around 600 calories per day, replace normal foods and are intended to kickstart your diet by providing concentrated nutrients in one low-calorie ‘meal’.

The plans may be used in different ways. Some use the meal replacements for up to a week without any food, whilst others use them for several weeks replacing one or two meals a day and eating a normal meal in the evening. Whilst they may be useful to those who are clinically obese or who can’t lose weight on conventional diets, it is important that these plans are never used for longer than four weeks. They are designed to help kickstart your diet only and don’t provide enough calories for long-term nutrition.

The Department of Health has expressed concern over the safety of these diets for people with heart and kidney disease, hypertension, cancer, diabetes and gout. They also advise against use for pregnant or breastfeeding women, infants, children, adolescents or elderly people.

Myth 3: Potatoes and other carbs are fattening.
Carbohydrate foods like potatoes, rice, pasta, and bread are not fattening unless you put fat (in the form of sauces or butter) on top of them. Carbs play an important role in diets since they satisfy our appetite without being too high in calories. Fats, however, are less satisfying and have over twice the amount of calories per gram as carbs (9 calories per gram compared to 3.75 calories per gram respectively). Because fat is less satisfying, we tend to eat more of it. A low-fat, high-carb diet is therefore more effective for weight loss because you stave off hunger by eating carbs and are less likely to overdo your fat intake.

Myth 4: Low-carbohydrate, high-protein diets are the best way to lose weight.
People who follow ‘low-carb’ diets (like every actress in Hollywood these days) tend to lose weight initially, but much of this weight is water. Since calories from carbs are the first thing our body uses for fuel, following a low-carb diet forces the body to quickly use this energy, then revert to stored carbs (known as glycogen) from the liver and muscles for energy. Since water is stored in the body with glycogen, you lose water as this glycogen is used for energy. Therefore most of the weight loss that occurs at this point is water and not fat.

Once these stored carbs are used up, the body then relies on protein for energy and as a result, compounds called ketones are produced. These can be dangerous, particularly for people with medical problems such as heart disease, hypertension, kidney disease, and diabetes because the brain relies on glucose for energy, but ketones don’t provide energy for the brain. The body therefore tries to eliminate ketones through the liver and kidneys, which puts a severe strain on these organs because of the toxicity of ketones to the body. For people with metabolic problems, ketones are particularly hard to metabolise and eliminate. Due to the high level of ketones produced in a low-carb/high-protein diet, you may also experience dehydration, weakness, nausea and, in severe cases, gout and kidney problems.

Additionally, many low-carb/high-protein diets can be problematic if the protein you eat is high in saturated fat (such as fatty bacon or cheese), because it increases the risk of heart disease. Despite the belief that carbs are fattening, fat is much higher in calories than carbohydrates. Current nutritional advice advocates a low-fat diet made up of 35% fat, 15% protein and 50% carbs, with most of your calories coming from starchy carbs.

Myth 5: Drinking water helps you lose weight.
Drinking water helps to keep you hydrated and fills you up without any calories, but it won’t help you burn calories. Water works well in combination with a sensible diet and regular exercise. With high-fibre diets in particular, water can keep your gut healthy by helping to move things through your system more quickly.

Myth 6: A diet is successful only if you lose more than two pounds a week.
Your main goal when trying to lose weight is to reduce fat rather than muscle. But if you lose more than two pounds a week you’ll also lose lean tissue (or muscle). Because your basal metabolic rate (or the speed at which you burn calories) is determined by the amount of lean tissue you have, less muscle means your metabolism slows down and it becomes difficult to sustain weight loss.

Myth 7: Diets based on single foods (i.e. the cabbage soup or egg diets) are the best way to lose weight.
Diets based on a particular food or food type promise rapid weight loss in a short period of time, but only work because they severely restrict calories. These diets are unsustainable long-term and can lead to deficiencies since single foods don’t contain the range of nutrients we need to stay healthy. The Academy of General Dentistry in the US suggests that certain diets like this can even negatively affect oral health since they lack nutrients like calcium and vitamin D, which are necessary for maintaining healthy teeth and gums.

Myth 8: Fat is a four-letter word
Fat is not bad for you. In fact, it is important to get 35% of your daily calories from fat (if you eat around 2000 calories a day, you’ll need about 70g fat). Fat has many crucial functions aside from being a concentrated source of energy. First, it circulates fat-soluble vitamins such as A, D, E and K through the blood so they can be absorbed by the body. Secondly, fat contains essential fatty acids such omega-3 and omega-6, needed for the proper formation of the nerve walls. Note: it’s better to eat poly- and mono-unsaturated fats (such as olive oil) which are good for your heart, than saturated fats (such as animal fats) which increase the risk of heart disease. Because fat is a concentrated source of energy, you don’t need to eat a lot of it. Here’s how to reduce your fat intake:

• Switch to lower fat versions of milk, cheese and other dairy products.
• Use leaner cuts of meat and remove skin from chicken.
• Use little or no fat in cooking.
• Grill, poach or steam foods instead of frying or deep frying them

Myth 9: Diet pills help you lose weight
There are hundreds of diet pills on the market that claim to help you lose weight, many of which contain extracts of chitosan (crushed up shellfish skeletons) and conjugated fatty acids (CLA’s). However, current scientific evidence does not suggest that diet pills help weight loss long-term. Some diet pills claim to be effective based on evidence from scientific studies conducted on rats, which is then extrapolated to humans.

The only evidence from a human study using chitosan showed that people did lose weight, but the subjects were also on a calorie-controlled diet, so the study’s efficacy is in question. In addition, the study highlighted the possibility that diet pills may interfere with the body’s ability to absorb fat-soluble vitamins, such as A, D and K, so anyone using diet pills containing chitosan long term may have a deficiency in these vitamins. As far as the effect of diet pills on your metabolism, the result is still unknown. Ultimately, whatever beneficial effects diet pills may provide in terms of weight loss, these benefits are lost when you stop using them, which most often results in weight gain.

Myth 10: If you stick to your diet, you don’t need to exercise to lose weight
To maintain your body weight, the calories you take in should equal the calories you expend, so the most effective way to lose weight is by reducing calories and increasing exercise. However, exercise is important even if you are not trying to lose weight, as it also improves cardiovascular health, circulation and decreases your risk of heart disease and diabetes. Doctors have stated that it is better to be fit and slightly overweight than thin and unfit, as physical activity is as important as weight in preventing heart disease.

If you’ve never exercised before or if you have a medical condition, it’s essential that you check with your GP before starting any exercise regime. Ultimately, you should aim to work out up to 30 minutes at least five times a week. It is advisable to start off slowly before building up to a more rigorous plan. For example, take the stairs instead of the lift or walk to the next bus stop instead of waiting at the stop. If you exercise and have a healthy diet, you will find it easier to lose weight and keep it off.